normally used on land for large units will certainly be tried at sea also.

A few examples shown below will demonstrate the thermal efficiencies obtainable with varying steam conditions and sizes of installations.

The fuel consumption of 0.4 lbs/BHPh published recently by Pametrada corresponds to the last efficiency. These figures show that by application of higher steam conditions and reheat the efficiencies of 25-27 per cent usual nowadays may be raised to 31-35 per cent, but this improvement has to be paid for by a considerable complication in the steam plant. The efficiencies indicated can only be obtained if the burners are perfectly adjusted in relation to the load, and the temperatures of the individual preheating stages, the superheater and the condenser are correctly maintained. Even small deviations will affect the efficiency. Furthermore partload efficiencies are considerably poorer for a steam plant than a diesel plant, the fuel consumption of which varies only by approximately 1 per cent throughout the normal operating range.

The metal temperature is limited to 550° C by the use of ferritic steel. Austenitic steels, which can stand higher temperatures, are not suitable as they are more sensitive to temperature variations and thermal shock.

The very high efficiencies of large land-based plants can hardly be reached in marine installations on account of their smaller size and the lack of space normal in ships, which precludes the use of the same ample heat transfer surfaces as in power stations. Furthermore marine installations create additional governing problems due to sudden load changes which may even affect the safety of the plant.

For all these reasons it will hardly be possible to obtain the optimum efficiencies measured on the test stand in actual operation at sea. They will have to be reduced by a few per cent. Furthermore

a certain reduction of the efficiency with operating time is usual. Neither diesel nor steam turbine will show sensational improvements in their efficiencies. Thus both steam and diesel will retain their leading position for ship propulsion, possibly on a somewhat higher level of development, as long as fuel oil is obtainable for them.

Gas Turbine

Basically the gas turbine appears to be the ideal prime mover for propeller drive. Compared with the steam turbine, there are no problems of feedwater or condensers, and there is no wear inevitable in the sliding parts of the diesel engine. It is also mechanically much simpler than the diesel engine, but unfortunately it is not able to burn ash-containing fuels at cycle temperatures of more than 650° C due to deposit formation and vanadium corrosion. This maximum temperature limits the total efficiency to 22-23 per cent or to 27-28 per cent if a recuperator is used. When clean fuels are used — whether petroleum distillates or even gases like methane, which is now transported in liquid methane carriers - the maximum cycle temperature is limited by the strength of the materials. With materials able to stand 850° C, 24-26 per cent or again with recuperation 33-35 per cent can be reached. With still higher temperatures, e.g. 1000° C, using blade cooling and clean fuel, efficiencies of 26-28 per cent without or 38-40 per cent with recuperation may be envisaged. Two-stage compression with intercooling would improve the efficiencies by 1 per cent without recuperation. With recuperation, however, 3-4 per cent would be possible at 650°, 2 per cent at 850°, and 1 per cent at 1000° cycle temperature.

These figures mean that at present with residual oil the only economically available fuel for ships the gas turbine efficiency is limited to a maximum of 30-32 per cent. Advanced plants using blade cooling and clean fuels may obtain efficiencies of about 40 per cent. Any metallurgical advance making higher cycle temperatures possible will improve the efficiency for both gas turbine and steam turbine.

Present State and Future of Automation in
Marine Power Plants

During the last few years, remote control of the main propulsion unit and auxiliary systems has been introduced using relatively simple methods. All the different systems in marine propulsion plants can easily be automated as long as a basic source of energy and accurate, reliable instruments for measuring temperatures,

pressures, etc., are available, which can be relied upon in full during long spells of service without frequent re-calibration. Since, however, at the moment no sensing and detecting equipment is available which can anticipate smaller discrepancies and react before major damage can occur, human supervision at regular intervals is still compulsory. The present stage of automation practice has already produced an important reduction of attendant engine-room personnel. A further step will be to organise the crew on a rota system, similar to airline practice, and the last step would be completely unmanned ships.

This progress will be parallel to the development of instrumentation and sensing equipment reporting the principal data to an outside operating centre and supplemented by a computer-controlled ship's installation operating to a programme or on orders received from that centre.

Even in carefully laid-out installations, incorporating sophisticated standby and automatic emergency systems, maintenance will nevertheless be required. But it will be necessary to organise scheduled maintenance only after longer intervals. For this work, however, highly qualified engineers will be required who will be stationed ashore, and who can be called upon in case of emergency by means of air transport.

Propeller

Without any doubt the propulsion methods will be improved. More frequently the propeller will be installed in nozzles or tunnels to improve the propulsive efficiency. Systems whereby water is taken from the boundary layer around the hull and accelerated in propelling jets will reduce the friction drag of the ship. Power also may be saved by the use of submarine freighters avoiding the surface wave resistance.

Oil Resources

The previous considerations are based on the availability of fuel oil. What is going to happen when the oil resources are exhausted? This moment is not as far away as is often believed. It will certainly be reached within the next 100 years. Professor Eichelberg has published recently the following conclusion (Schweizerische Bauzeitung, 5/8/65). The oil reserves on the North American Continent are best known and will serve as a basis for further estimates. Up to now a total of 9,000 m tons have been extracted there, and a further reserve of 4,000 m tons is known today. In addition to this some 2,000 m tons may still be found. Increasing this total by 50 per cent, which might still be gained by improved

production methods, including secondary recovery of oils as yet unpumpable, a total of 22,000 m tons might be expected. Assuming the same concentration of oil deposits for the whole dry surface of the earth, including the continental shelves, a total world reserve of 160,000 m tons would result.

Assuming furthermore a continuous doubling of consumption every 10 years, as has been the case up to now, then the total world reserve would last only 30 years. Even if the consumption were limited to a level attained in 1975 this means twice the present figure the reserves would be exhausted in 50 years. Other estimates, pessimistic and optimistic ones, place the total reserves in the range of 100-300,000 m tons, confirming the estimate of 160,000 m tons. Even if this figure were twice as high, the reserve would last only some 10 years longer as consumption keeps on doubling every decade. These figures may not be absolutely correct, but they are alarming, and the fact remains that the earth contains only a limited and irreplaceable amount of oil. What after it is spent?

Coal will be available for a much longer period. Of course, it could be used again in marine boilers, but this would be very undesirable due to all the complications involved. More probable will be the production of synthetic liquid hydrocarbons from coal. Petrol, diesel fuel, heavy fuel and lubricating oils may be manufactured from coal. This has been done on a large scale with the Bergius and Fischer-Tropsch processes, and is still going on today. Thus it would be possible to continue operation to a certain extent with the same types of propulsion plants as nowadays.

Possibly also fuel cells may be developed by then to a stage where synthetic fuels of sufficient purity may be used to obtain electricity directly from chemical energy. This would result in a marine propulsion plant of optimum simplicity, as the thermal component whether engine, steam- or gas-turbine would be eliminated. However, mentioning this possibility does not answer the question: What happens when there are no more fossil fuels available for combustion? What other sources of energy are available on this planet?

Wind energy. There will hardly be a return to the sailing ship. Water energy. Not suitable for marine propulsion. Solar energy. Unsuitable for marine propulsion as the radiation density is small and would require surfaces of impractical size to be exposed to the sun.

Only nuclear energy remains. Here it must be borne in mind that present reactors utilise only a small portion of the energy contained in their fuel, and the uranium quantities available now would not last for very long. For this reason breeder-type reactors will have to be employed, which convert non-fissile elements into fissile ones. The heat energy produced in reactors would be utilised in steam

turbines or closed-cycle gas turbines. Possibly means of obtaining electric energy directly from atomic power might be found.

The direct application of atomic energy would mean that every ship would carry its own reactor on board. It is a frightening thought that thousands of ships will be circulating on the seven seas, each one equipped with an atomic reactor, each with its safety installations, its radiation shields, etc., and still carrying the potential danger of atomic contamination in case of a collision. Changing "hot" fuel elements and dumping them in a shielded water pool until their radiation has subsided sufficiently would be complicated, but could be visualised. Ships of the future may be built much bigger in order to reduce their number and thus the probability of accidents. Of course only dry cargo vessels would be needed, as there would be no need for tankers due to lack of oil.

The transport of goods would probably be done in containers in order to reduce harbour time. Another proposed way to reduce the number of atomic reactors afloat would be the design of "ship trains" having a nuclear-powered tug as a "locomotive ", pulling or pushing a set of large barges.

Another possibility thought of already would be a floating atomic power plant, producing electrical energy and delivering it by cables to a convoy of ships driven by electric motors. Such ships might be even completely unmanned, steering their way and keeping the correct relative positions and distances by electronic means. Even navigation of the whole convoy might be automatic by using satellites as reference points. Such trains or convoys would probably not enter the ports any more but would drop the corresponding unit outside and pick up another one, which would be manoeuvred in and out of ports by harbour tugs. How these tugs might be driven will be discussed later.

Again impelled by the danger of a large number of atomic reactors afloat, means ought to be found to utilise atomic energy indirectly for marine propulsion. Large atomic power stations on shore will produce electric power in any desired amount. It would be a decisive advance if batteries of sufficient capacity could be developed, small and light enough to be installed on board. They could be charged in port and the ship would be driven by electricity. This would be an extremely simple method of propulsion, containing all the prerequisites for an unmanned vessel.

Another method leading in the same direction of indirect utilisation of atomic energy would be the following: on shore hydrogen would be produced by electrolysis; delivered to the ship in liquefied form this hydrogen could be used in fuel cells, in gas turbines or gas engines. In respect of weight, liquid hydrogen contains 2 times more heat value than fuel oil, but to carry the same calorific value as diesel fuel roughly five times the volume for storage tanks is